1. Technical Field of the Invention
The present invention relates to a gas sensor that senses the concentration of a specific gas in a gas to be measured.
2. Related Art
A gas sensor 9 as shown in FIG. 14 has been known, which senses the concentration of a specific gas in a gas to be measured (hereinafter referred to as a “measurement gas”). This type of gas sensor is disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 2003-185620.
Such a gas sensor 9 includes a gas sensing element 92 that senses the concentration of a specific gas in a measurement gas, a housing 93 having an interior through which the gas sensing element 92 is passed, and an element cover 94 consisting of an inner cover 941 and an outer cover 942, which are secured to the tip end side of the housing 93.
In order to reduce the probability of getting wet with water (hereinafter referred to as “water resistance” (anti-wettability)) of the gas sensing element 92, a gas sensor 9 as shown in FIG. 15 has also been suggested. This type of gas sensor is disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 2003-161717.
An element cover 94 in such a gas sensor 9 has an inner cover 941 covering a gas sensing element 92, and an outer cover 942 disposed outside the inner cover 941. The inner cover 941 has inner charge ports 941a formed in its side wall body and an inner discharge port 941b formed in its bottom body. The outer cover 942 is disposed surrounding the outer periphery of the inner cover 941 and provided with side openings 942a formed in its side wall body and with a discharge opening 942b formed in its bottom body.
As shown in FIG. 16, in forming each of the side openings 942a, the side wall body of the outer cover 942 is cut into substantially a “U” shape to obtain a cut piece 944 inside the “U” shape. Then, the tip end portion of the cut piece 944 is radially pressed inward so as to be bent inward about its base end portion to thereby form the side opening 942a. 
Each side opening 942a is open along the U-shaped cut line. Thus, the direction to which the opening face faces, i.e. the opening direction of the opening, is adapted to have components directed toward the axial tip end side of the gas sensor 9 as well as components directed to the circumferential direction of the gas sensor 9.
However, such a conventional type gas sensor 9 has suffered from the problems as set forth below. Specifically, as mentioned above, the conventional type gas sensor 9 is formed so that the opening direction of each side opening 942a will additionally include the components directed to the circumferential direction. Therefore, after entry from the side openings 942a, water that flows through the exhaust pipe together with the measurement gas may tend to directly go into the circumferential direction through the space between the outer cover 942 and the inner cover 941 and may tend to enter into the inner cover 941 through the inner charge ports 941a. Therefore, there has been a concern that the gas sensing element 92 may get wet, causing cracks at the portions that have gotten wet with the water.
One measure that can be taken may be to find the best positions of the inner charge ports 941a in the inner cover 941 so that the gas sensing element 92 may hardly get wet. In this case, however, it is likely that the responsiveness of the gas sensor 9 may be deteriorated.